This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Recently NIR spectral absorption signatures that may be specific to pathology in breast tissues have been discovered. These spectra, referred to as "Specific Tumor Components", or STC spectra, have been shown to distinguish between benign and malignant breast lesions. In this previous work, STC spectra from tumors were averaged together to provide a tumor STC. However, tumors are known to be heterogeneous in structure and function. We propose that heterogeneity in the STC spectra within a given volume of tissue may be indicative of the spatial distribution of distinct cellular populations within the tumor. Characterizing the types of spectral heterogeneity might therefore predict the response of the tumor to therapeutic interventions.